ATLAS Minimum Bias Trigger Scintillator Upgrade for LHC RunII A. - PowerPoint PPT Presentation

ATLAS Minimum Bias Trigger Scintillator Upgrade for LHC RunII A. Sidoti Istituto Nazionale Fisica Nucleare – Sezione di Roma “La Sapienza” on behalf of the ATLAS Collaboration 1

Outline Minimum Bias Trigger Scintillators (MBTS) in Run I (2009-2013): Physics motivations Physics potential Performance Upgrade for Run II (2015-): Design Construction T ests 2

The ATLAS Detector pp collisions at √ s=0.9, 2.36, 7 and 8 T eV LHC in operations from 2009-2013 Heavy Ion collisions (HI): → Now in shutdown (LS1) PbPb collisions at √ S NN =2.76 T eV → Back to operations in 2015 pPb collisions at √ S NN =5.02 T eV beam beam 4

Few years before LHC start up, ATLAS realized that a subdetector able to trigger on genuine low luminosity collision events would be crucial Requirements: Sensibility to single low momentum particles → Calorimeter T rigger at Level 1 with high effjciency→ Inner Detector Tight time and installation constraints could only allow for a simple detector which could be read out by existing electronics → The solution: scintillators from JINR (polystyrene, same slabs as preshower and Muon Extension for CDF) - Instrumentation and readout electronics from Tile Calorimeter 4

The ATLAS Detector beam ATLAS Tile calorimeter layout beam

The ATLAS Detector p,Pb beam

The ATLAS Detector 8 x 2 Plastic WLS fjbers Scintillators 4+4 / 4+4 89 cm 15.3 cm p,Pb beam

 The ATLAS Subdetectors From G. Wolshin EPL 95 61001 (2011) 7 T eV 14 T eV dN/d η (au) EMEC EMEC 2.36 T eV FCAL FCAL LUCID ALFA ALFA LUCID 0.9 T eV BCM BCM MBTS MBTS ZDC ZDC ID Detector Detector η coverage η coverage ID (Pix + SCT) | η |<2.5 BCM | η |=4.2 ID (TRT) | η |<2.0 LUCID 5.6<| η |<6.0 MBTS 2.08<| η |<3.75 ZDC | η |>8.3 Calo: EMEC 2.5<| η |<3.2 ALFA(RP) 10.6< |η |<13.5 8 Calo: FCal 3.1<| η |<4.9

Signal path: from scintillators to Central Trigger Processor ATLAS Cavern (UX15) MBTS Scint. 3in1 PMT ADC LG Adder Digit Boards HG ADC ATLAS Underground “Counting Room” (USA15) Adapter Boards Leading CTP Edge (in Run I) Constant Fraction (for RunII) 8

First Collision from LHC First ATLAS registered in ATLAS C a l o r i m e t e r MBTS Inner Detector 10

Run I Physics Results Based on MBTS Excerpt of RunI ATLAS Papers based on MBTS: Soft QCD Physics and Heavy Ion Measurement of underlying event characteristics using charged particles in pp collisions at sqrt(s) = 900 GeV and 7 T eV with the ATLAS Detector, Measurements of underlying-event properties using neutral and charged particles in pp collisions at 900 GeV and 7 T eV with the ATLAS detector at the LHC, Charged particle multiplicities in pp interactions Measurement of the Inelastic Proton-Proton Cross-Section at sqrt(s) = 7 T eV with the ATLAS Detector Rapidity gap cross sections measured with the ATLAS detector in pp collisions at sqrt(s) = 7 T eV Measurement of inclusive jet and dijet production in pp collisions at sqrt(s) = 7 T eV using the ATLAS detector Measurement of the centrality dependence of the charged particle pseudorapidity distribution in lead-lead collisions at sqrt(s_NN) = 2.76 T eV with the ATLAS detector Observation of a Centrality-Dependent Dijet Asymmetry in Lead-Lead Collisions at sqrt(S(NN))= 2.76 T eV with the ATLAS Detector at the LHC and more and more 11 Crucial to get the correct UE tuning for MC at √s=13 T eV

Inelastic pp Cross Section Measurement Asymmetric events: → Measure R ss : ratio of single sided MBTS events wrt total inelastic events From R SS Measurement → Extract f D ratio 12

Inelastic pp Cross Section Measurement f D predicted from R ss according to several models (main uncertainty) 13 Constraints of the various models based σ inel =69.1 ±2.4(stat)± 6.9 (extr) mb on MBTS multiplicity Nature Communications 2 , 463, (2011) 13

Run I Performance (900 GeV and 7 T eV Collisions) 2009 Data √s=900 GeV MBTS T rigger effjciency as a MBTS Trigger effjciency as a function of single track φ function of track multiplicity – Start of LHC Run I (2010) ~1 Effjciency for small track multiplicities Excellent charge collected Data-MC agreement (after MC Calibration) 14 ATLAS-CONF-2010-068 (7 T eV) 14 ATLAS-CONF-2010-025 (900 GeV)

Extending to Heavy Ions Running Trigger using difgerent MBTS multiplicities b P b b P P p Difgerent physics processes: PbPb collisions in 2011, pPb collisions in 2013 rigger using difgerent Difgerent hardware settings MBTS multiplicities (thresholds, PMT HV) ~30 fb -1 of pp collisions until 2013 data taking → Still good single track 15 performance T ATLAS-CONF-2012-122 15 ATLAS-CONF-2013-104

Run I Performance α : exponential signal slope Fit e - α x Inner MBTS Modules Outer MBTS Modules 5 fb -1 of pp collisions between September 2012 and January 2013 measurements Slightly changed LE threshold values and PMT HV → Same physics process (pPb collisions) 16 Threshold LE Discriminator value ATLAS-CONF-2013-104

Radiation Dose @10 4 Gy → ~50% Loss Light Transmission Ionization dose (Gy) prediction after 1 year at MBTS position 10 34 cm -2 s -1 at √s=14 T eV In Run I MBTS accumulated ~0.21 x (0.5-2.0)x 10 4 Gy = [0.1~0.4] x 10 4 Gy 17

MBTS in Run II Decided to keep the same Run I readout scheme → Instrument Tile crack scintillators → need to reduce number of channels used by MBTS Instead of 16 x 2 channels use 12 x 2 channels. Reduced granularity for outer disks (4 per side) → Coupling of optical fjbers from adjacent scintillators Kept same granularity for inner disks (8 per side) → Maximum care to guarantee the same light yield than in RunI 18

MBTS in Run II Decided to keep the same Run I readout scheme → Instrument Tile crack scintillators → need to reduce number of channels used by MBTS Instead of 16 x 2 channels use 12 x 2 channels. Reduced granularity for outer disks (4 per side) → Coupling of optical fjbers from adjacent scintillators Kept same granularity for inner disks (8 per side) → Maximum care to guarantee the same light yield than in RunI 19

MBTS: Run I vs Run II Design η =3.75 η =3.86 η =2.78 η =2.76 η =2.08 η =2.08 RunI RunII Black paper to avoid cross-talk Fiber grooves (depth = 4.5 mm) (Kuraray Y11 (200) MSJ) 4 fjbers on each side (8) for large scintillator 20 4 fjbers for small scintillator Connection fjbers Bicron BCF -98 (1mm) Slight geometry change in Run II (increase η coverage)

MBTS Run II Construction MBTS side A already installed 21 MBTS side C to be installed before May 2014 Upgraded system will join ATLAS common 20 cosmics data taking in July 2014

MBTS Side A Installed! 22 21

MBTS Run I vs Run II Light transmission checked with Sr90 source T est scintillator and fjbers moving the Sr source on the scintillator surface 23 → precise relative map of light transmittance

MBTS Run I vs Run II r(mm) Inner MBTS scintillators Run I: Moderate R dependence on irradiated sample → Damage from radiation under x(mm) control (or recover) Run II: r(mm) → more uniformity Expected light yield wrt Run I: larger for inner scintillators ~similar for outer ones → Full light yield depends on x(mm) the full optics path Relative check of light transmission 24

Cs Scans Blue: Inner Counter All MBTS counters have been Red: Outer Counter scanned with Cs scan setup Outer Checks performed on optics Inner Detector Detector quality and response checks of every scintillator assembly before installation. Position of Cs probe 25 Approximate position of tubes for Cs-137 source 23

Modifications from Run I Refmections → causing large accidental rates From adapter boards for trigger signal impedance mismatch Before the input impedance fjx After the input impedance fjx Use Constant Fraction Discriminator 26 Large signal variations time walk fjx

Conclusions MBTS upgrade for Run II is progressing well → Crucial to trigger on “Soft QCD” physics events during fjrst Run II LHC fjlls → MBTS still useful for all low luminosity LHC fjlls Damage from radiation seems under control Adjustment of electronics to fjx issues sufgered during Run I operations In the remaining part of 2014 (before LHC start up) → optimization of PMT HV and thresholds → Cosmic test stand → Join ATLAS common cosmic data taking (from July 2014) 27

BackUp 28

The ATLAS Forward Detectors (LHC Run I) 29

The ATLAS Forward Detectors (LHC Run II) 2 ? ? ? ? 2 AFP 30

Experimental T ools II: Rapidity Gaps For ND events dN/d η (@P T >100 MeV, √ s=7T eV)~6 → < η j - η k >~0.15 (cf G. Brandt talk) Larger η gaps are exponentially suppressed except for Difgractive events Measuring ∆η is a measurement of M X(y) Diffjcult measurement of M X(Y) → Produced particles escape undetected in the beam pipe η acceptance is defjned in the largest η range -4.9< η <4.9 → However max η gap determined by MBTS position (→ trigger) (Max ∆η ~8) Using ID+EM+HEC+FCAL Experimentally (detector) η rings (variable width 0.2, 0.4 according to η region): Active ring if: At least one track with P T >200 MeV (also P T threshold=400,600,800 MeV/c) At least one calorimeter cell above noise threshold ( η -dependent threshold, no noise in Tile) and E T cut (same as track) 31